Using plasma for cleaning, etching, film formation, etc., has been conventionally known.
Patent Document 1 discloses a plasma treatment system for providing stable electric discharge into air without using helium gas, which includes a reaction tube for supplying a reaction gas and first and second electrodes facing each other with the reaction tube located therebetween for acting on the reaction gas. In this system, high frequency power is supplied to the first and second electrodes such that the reaction gas is excited to generate plasma, and a target substrate is treated with the generated plasma.
Patent Document 2 discloses a system for generating uniform discharge plasma under a near-atmospheric pressure irrespective of the type of a gas atmosphere used for treatment. This system includes electrodes facing each other, wherein at least one of the electrodes has a facing surface provided with a solid dielectric, and a pulsed electric field is applied between the electrodes.
The technique disclosed in Patent Document 1 is characterized in that the reaction gas flowing through the reaction tube is converted to plasma which is, in turn, sprayed out of the reaction tube onto a target. The technique disclosed in Patent Document 2 is characterized in that the surface of the target placed on the second electrode plate is treated. Both of these techniques are directed to a surface treatment with the intention that it is carried out with a relatively large device.
On the other hand, using plasma for sterilization and disinfection has been studied. Examples of the conventional medical sterilization actually in practice include high-pressure steam sterilization, ethylene oxide gas sterilization and disinfection as well as peroxide gas sterilization. These have the problems of high temperatures, use of dangerous gas (ethylene oxide gas), unavailability under atmosphere, degassing as long as one week or more, etc. Plasma sterilization systems disclosed in Patent Documents 3 to 5 are directed to sterilization of the cavity of a narrow tube, for which only a few practical sterilization methods have been conceived.                Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-184759        Patent Document 2: Japanese Laid-Open Patent Publication No. 10-154598        Patent Document 3: Japanese Laid-Open Patent Publication No. 2003-135571        Patent Document 4: Japanese Laid-Open Patent Publication No. 2003-210556        Patent Document 5: Japanese Laid-Open Patent Publication No. 2005-46264        